Conventionally, there are known car antitheft systems, usability improvement systems, and accident prevention systems. As will be discussed below, such systems recognize driver's appearance for individual authentication, closed-eye detection, and the like using vehicle driver's face images captured by a camera.
For example, an individual authentication system using face images extracts a pupil's iris pattern from driver's face images captured by a camera. The system collates the extracted pattern with a previously registered iris pattern (e.g., see Patent Document 1).
When both patterns match, user recognition control means allows an engine to start in order to use the individual authentication for protecting the car against theft. Alternatively, the environment such as in-vehicle units is configured for a user in order to use the individual authentication for improving the usability.
As another technical field, there is known a face authentication system (e.g., see Non-Patent Document 1) to ensure the security management of entry to or exit from rooms such as offices.
In this face authentication system, for example, the user recognition control means uses a camera to capture shading such as face images and identifies the shading as a feature quantity attributed to an individual. The system collates the feature quantity with a previously registered feature quantity to implement the individual authentication. The feature quantity represents shading patterns, the gradient amount of shading changes, and the like, in the vicinity of facial parts.
In a closed-eye detection using face images, for example, closed-eye detection means extracts an eye portion from the face image captured by a camera. The system chronologically detects whether the eye is opened or closed based on the number of pixels between upper and lower eyelids.
The system uses determination means to determine whether or not a driver falls asleep at the wheel based on a detection result from the closed-eye detection means (e.g., see Patent Document 2).
These systems to recognize the user appearance using face images generally have infrared light radiation means such as a light emitting diode. When a camera captures images, the infrared light radiation means radiates infrared light to a user's face.                Patent Document 1: JP-2000-168502A        Patent document 2: JP-H6-32154A        Non-patent Document: “Face authentication” by OMRON.        
The present invention relates to a system which can be mounted on a vehicle capable of performing both the above-mentioned individual authentication and closed-eye detection using face images.
In this case, however, some of the above-mentioned individual authentication technologies identify shading in a face image to be feature quantity attributed to individuals. Such technologies cause the following problem.
As mentioned above, the individual authentication and the closed-eye detection using face images both use a camera to obtain face images by radiating infrared light. Accordingly, the camera, the infrared light radiation means, and the like can be shared.
Generally, the infrared light radiation means such as a light emitting diode is used to apply a specified current and provide constant illumination intensity. Current supply means supplies the infrared light radiation means with a constant current to provide specified illumination intensity. For this purpose, the current supply means is previously assigned a current value to be supplied to the infrared light radiation means.
Let us consider a case of mounting the system for performing the individual authentication and the closed-eye detection using face images on a vehicle by sharing the infrared light radiation means. It is necessary to set an electric current value supplied to the infrared light radiation means so that its illumination intensity can comply with the individual authentication requiring high illumination intensity.
The individual authentication requires a higher illumination intensity than the closed-eye detection for the following reason. Feature quantities need to be strictly detected on an individual authentication system that identifies shades in a face image to be the feature quantity attributed to an individual.
However, for example, the feature quantity varies with face images when the light is applied to the entire face and when the west sunlight is applied to a half of the driver's face in the evening. For this reason, the above-mentioned individual authentication system requires somewhat controlled illumination environment so that the constant feature quantity can be obtained from face images.
On the other hand, the closed-eye detection system just requires the illumination intensity so controlled as to be able to capture an eye's outline and detect the eye's inside movement.
Accordingly, when the illumination is radiated to the driver's face for image acquisition, the necessary illuminance is higher for the individual authentication than for the closed-eye detection. For this reason, the infrared light radiation means needs to be supplied with a current value large enough to provide the illumination intensity needed for the individual authentication.
The closed-eye detection aims at preventing drivers from falling asleep at the wheel. Accordingly, the closed-eye detection is always performed while a driver is driving the vehicle.
When the same vehicle is equipped with the system to perform the individual authentication and the closed-eye detection using face images, a large current must be applied to the infrared light radiation means for capturing driver's face images using the camera. The current is continuously applied while the driver is driving the vehicle.
Generally, applying large currents shortens the service life of the infrared light radiation means such as the light emitting diode. When a vehicle is equipped with the system to perform the individual authentication and the closed-eye detection using face images, the service life of the infrared light radiation means becomes short.
Such problem is not limited to the case of equipping vehicles with the system performing the individual authentication and the closed-eye detection. The problem also occurs in a system to perform a plurality of appearance authentications differing in necessary illumination intensities on face images used for the driver's appearance recognition. The problem becomes particularly remarkable for the case of equipping a vehicle with the individual authentication system and the closed-eye detection. That is, the former is a function that needs to strictly detect the face image's feature quantity. The latter is a function that need not strictly detect the face image's feature quantity.
There is known a method of decreasing the amount of current applied to the infrared light radiation means in order to prolong its service life. However, this method is unpreferable because the infrared light radiation means generates low illumination intensity and decreases the detection accuracy during the individual authentication.